The present invention concerns a clasp for assembling two flexible strands, for example made of leather or a synthetic material. Such a clasp may be used, for example, for a watch strap or wristband, or a belt.
In known clasp devices for assembling flexible strands, the strands include holes provided to receive a tongue when they are assembled. This conventional construction has, however, the drawback that said strands break easily, generally where the hole receiving the tongue is located, because of the fatigue to which such strands are subjected.
Wristbands or bracelets, particularly those which are fitted to watches, need to be able to be closed on the wrist easily and without there being a risk that the watch can slip away when one tries to form the fastening loop. For this reason, the wristband can be continuous so that it remains securely on the wrist.
A first known solution relates to wristbands formed of contiguous metal segments which contain small springs which allow the wristband to be extended when it is pulled. In order to be able to work, such a solution however requires very small springs subject to fatigue and which have a limited life time.
In order to overcome this drawback, claps with multiple articulated hinges have been proposed, these claps being essentially mounted on metal bracelets with two articulated but non-extending segments. This more advantageous solution was obtained with continuous devices with segments which are rigid, articulated, folding, able to be superposed and caught on each other. A very large number of models exists.
A model with three rigid segments may be cited as an example, the first of which closes under the second, while the third, acting as a cover, engages on the second and locks onto the first.
These conventional clasps with unfolding buckles have the advantage of preventing, to a certain extent, the wristband surreptitiously passing over the hand if a pulling force is exerted on the wristband. However, this type of clasp is relatively complicated and implements numerous parts, which makes it quite expensive.
A considerable improvement was made by the device disclosed in Swiss Patent No. 530,189 which proposed a construction which, while proposing a more attractive appearance, also improved the facility of fastening.
This device is formed of a clasp secured to one of the strands of a wristband and provided with means gripping the other strand of the wristband. This second strand is gripped between the base of the clasp and an eccentric end of a lever pivoting on the base of the clasp. The base plate of this clasp carries a rib which engages in one of the grooves made on the invisible face of the wristband intended to be in contact with the wrist of the person wearing the watch. Said base plate also carries a pin which engages in one of said grooves made on the invisible face of the wristband.
One advantage of this clasp lies in the fact that, in the embodiment described hereinbefore, the second strand engages under the first strand, which gives the wristband a very attractive appearance.
Another advantage is the great simplicity of construction of the clasp which allows its manufacturing costs to be substantially reduced. This clasp also has the advantage of being able to be fitted to any type of flexible wristband, for example of the Milanese or woven type, or those made of plastic material.
The clasp disclosed in Swiss Patent No. 530,189 has, however, a certain number of drawbacks from among the most important of which can be cited the fact that the pivoting lever which, via its eccentric end, grips the second strand of the wristband against the base of the clasp does not ensure that the wristband is firmly secured to the wearer""s wrist. Indeed, an external pulling force can very easily cause the lever to pivot into the opening position and cause the wristband to pass over the hand without such action being desired by the wearer. This method thus reduces the confidence which this type of clasp can inspire.
On the other hand, as was described hereinbefore, the base plate of the clasp carries both a rib and a pin which each engage in one of the grooves made on the lower face of the wristband. Since there is nothing provided to raise the wristband in order to free the grooves from their grip with the rib and the pin, the wearer will encounter significant difficulties in slipping the second strand out of the clasp when he wishes to take the watch off. This operation is made all the more difficult by the fact that the wristband is engaged with the base plate, not at one point, but at two distinct points materialised by the rib and the pin.
Finally, by gripping the wristband against the base plate of the clasp, the eccentric lever has the effect of marking the surface of the wristband.
Swiss Patent No. 454,513 discloses a watch wristband including a clasp secured to one of the strands of the wristband and provided with means gripping the other strand of the wristband. The gripping means are formed by a slightly curved plate, having a bottom provided on each side, in the direction parallel to the length of the wristband, with a perpendicular edge. A bar fixed in the edges assures the connection of the clasp to one of the wristband strands. A cover is hinged on the gripping means and pivots about the same bar as that via which the clasp is connected to one of the strands. On each side, in the longitudinal direction to the length of the wristband, the cover has an edge. These edges are slightly inclined inwards, like the edges of the plate, so that when the cover is closed, a certain resistance has to be overcome, which prevents the cover being opened inadvertently. The plate has a projecting part directed upwards which is engaged in one of the grooves arranged in the invisible lower face of the second wristband strand. When the cover is open, the end of the second strand is engaged in an opening of the clasp. The second strand is then adjusted to the desired length, then the projecting part is engaged in one of the grooves. Finally, the cover is closed.
This embodiment has the major drawback of wearing out quickly and no longer assuring that the cover snap fits properly on the edges of the clasp plate. This is essentially due to a high snap fitting force and, therefor, rapid wear of the system. If the clasp cover is not closed properly, an external pulling force may very easily cause it to pivot, so that the user is liable to lose his watch.
On the other hand, there is nothing provided to raise the second wristband strand under the lower face of which are arranged the grooves in which the projecting part of the plate has to engage. The user is thus liable to experience great difficulty in sliding the two wristband strands in relation to each other, since one of the strands is liable to be held back by the projecting part engaged in the corresponding groove.
The object of the present invention is to overcome the aforementioned drawbacks in addition to others by proposing a clasp for assembling two flexible strands, able to be used for example for a watch wristband or a belt, this clasp being inexpensive to make and very easy and secure to use.
The present invention thus concerns a clasp for assembling a first and second flexible strands including a buckle attached to the first of the two strands while the second strand penetrates the buckle, characterised in that the buckle includes fixed catching means which are caught in the second strand, and in that it includes an unlocking device able to be actuated manually, this unlocking device allowing the second strand to be raised to release it from the catching means and to slip it out of the buckle.
As a result of these features, the present invention provides a clasp which is easy to use. Indeed, in order to assemble the flexible strands of the wristband or belt and to close the clasp, one need only engage the end of the second strand in the clasp, so that this end is placed above the catching means. The wristband strand is then adjusted to the desired length, then the catching means are caught on the strand. The wristband is thus securely held in place and is not liable to be opened inadvertently. In order to open the wristband, one need only actuate the locking device manually. On doing so, the unlocking device raises the second wristband strand to release it from the catching means, so that the wearer need only pull on this strand to slide it with respect to the first strand and release it from the buckle.
The clasp according to the invention also offers great operating security. Indeed, as described hereinbefore, when the catching means are caught in the second strand, it is impossible to pull the second strand backwards. The confidence which one can have in the clasp according to the invention is further increased by the fact that the clasp does not require any parts to grip or clamp the second wristband strand in order to immobilise it. Consequently, the user is not liable to lose his watch as is the case with clasps of the prior art provided with gripping or clamping parts which are able to open inadvertently at any time.
According to a complementary feature of the invention, the catching means include a tooth, and the unlocking device includes a lever mounted so as to move on the buckle and which is capable of raising the second strand.
The clasp according to the invention thus only includes two parts, namely the actual buckle which carries a tooth which catches in the second strand and which, if desired, may be made in a single piece with the buckle or constitute a separate part which will be fixed onto the buckle, and the unlocking device which allows the user to raise the strand in order to release it from the tooth. In addition to the fact that the clasp according to the invention is very simple to use, it also has the advantage of only using a small number of parts and thus being inexpensive to manufacture.